1) In Premiere Elements 11 there are two tools to control time in a video. First is Time stretch in which you can choose a speed or the time in which you want to play the video.

Second is Time Remapping. This tool gives you better control over the time flow in a video. You can select multiple sections in a video and apply different speeds on them.To Access this tool you need to select the clip on the timeline and then launch Time remapping from Tools menu.

Please note that Audio of the clip will remain unchanged after applying time remapping.

2) This is by design. Clips on other tracks will move if change the speed using time-remapping or time stretch.